1. Field
The following description relates to an equalization technology for a coherent optical receiver used in optical communications.
2. Description of the Related Art
Coherent optical communication is a type of communication method that performs signal reception in a manner that input optical signals interfere with an optical source of a local oscillator signal and intensity variation and phase variation of the optical signals and phase variation are detected.
The coherent optical communication achieves higher receiver sensitivity and is more robust against noise such as amplified spontaneous emission (ASE) as compared to direct detection, and as such coherent optical communication has garnered a large amount of interest and many studies have been undertaken recently on this technology.
In general, an optical receiver for a coherent optical communication is provided with an optical phase-locked loop (PLL) or an optical polarization controller to process received optical signals. In addition, the optical receiver may be provided with an equalizer to compensate for impairment occurring on an optical path, such as chromatic dispersion and polarization mode dispersion.
In order for the optical receiver to process optical signals, a configuration to control a phase or a polarization of light is required. In general, the phase control or the polarization control has been performed in optical domains. However recently, with the development of digital signal processing technologies, an attempt to control phase or polarization of light has been made in a digital manner.
Meanwhile, for the purpose of synchronization of received signals in the optical receiver, a clock signal is recovered from the received signal and the received signal is recovered based on the recovered clock signal.